In general, various linear type valves are installed to be connected to valve switches. As a valve switch operates, a valve gate moves vertically to open/shut a path of flow of a fluid.
A linear type valve operates at the same time when a valve switch operates. Valve position measuring apparatuses are various. Preferably, a valve position measuring apparatus may be installed to be connected to a valve, to control a valve position based on a value of the valve position as measured.
An absolute majority of conventional valve position measuring apparatuses are structured to be connected to only a valve with a switch to move a valve gate vertically by operation of an electric motor. Therefore, most conventional valve position measuring apparatuses are limited in use.
That is, a conventional valve position measuring apparatus is installed to be connected to a rotary shaft of an electric motor. The valve position measuring apparatus measures the rotation number of the electric motor when a valve is open or shut, calculates a value of a valve position based on the rotation number of the electric motor, and indicates the value on a display.
Therefore, the conventional valve position measuring apparatus cannot be used in any other valves in which a valve gate moves vertically by operation of a hydraulic cylinder than the valve with a valve switch and an electric motor.
These days, a method for measuring a valve position by using a linear potentiometer has been suggested. The linear potentiometer is installed on a hydraulic cylinder. In this method, a valve position is measured based on a vertical movement distance of a piston rod which moves vertically in the hydraulic cylinder. The vertical movement distance of the piston rod is measured by the linear potentiometer. However, since the linear potentiometer is very expensive, the cost of production is high. Moreover, the work of installing the linear potentiometer is very complicated. In addition, since the linear potentiometer occupies considerable space, the volume of a valve position measuring apparatus is large.
Therefore, the present invention has been made to solve the aforementioned problems of a conventional valve position measuring apparatus, and to provide a linear valve position measuring apparatus, whereby a valve actual position is measured by measuring a rotation angle of a rotation sleeve which forwardly/reversibly rotates, depending on a vertical movement of a piston rod, and by calculating a movement distance of the piston rod (i.e., a movement distance of a valve gate) which changes in proportion to the rotation angle.
In accordance with an aspect of the present invention, there is provided a technique of measuring a valve position, by installing a rotation sleeve so as to be rotatable on a hydraulic cylinder, the rotation sleeve surrounding the outside of a piston rod; connecting a guide pin so as to protrude outwardly through a spiral groove formed on the rotation sleeve, the guide pin installed at an upper part of the piston rod; and installing a potentiometer at a top end of the rotation sleeve, the potentiometer outputting an electrical signal corresponding to a rotation angle of the rotation sleeve, wherein an electronic control unit (ECU) calculates a vertical movement distance of the piston rod by using the electrical signal of the potentiometer.
In accordance with another aspect of the present invention, there is provided a technique of preventing the guide pin from rotating when the piston rod moves vertically, by positioning the guide pin between a pair of supporting poles which are vertically installed.
In accordance with another aspect of the present invention, there is provided a technique of fitting a rod cap connected to a top end of the piston rod into a pin holder where the guide pin is installed, so that the rod cap freely rotates in the pin holder.
In accordance with the present invention, the potentiometer outputs the electrical signal corresponding to the rotation angle of the rotation sleeve which is operatively connected to the piston rod moving vertically and rotates, and the ECU calculates the vertical movement distance of the piston rod, thereby providing the effect of accurately measuring a valve actual position.
Consequently, the valve position is accurately measured by a simple method. Further, the structure of the valve position measuring apparatus is simplified. In addition, since an inexpensive component (potentiometer) is used, the cost is significantly reduced. Furthermore, since the linear valve position measuring apparatus is easily installed on the hydraulic cylinder, the work of installing the apparatus and the convenience are improved.